1. Technical Field
The present invention is directed to encoding and decoding images, and more specifically to an apparatuses and methods for encoding/decoding images that may be applied to intra prediction.
2. Description of the Related Art
In general image compression methods, one picture is separated into multiple blocks each having a predetermined size. Inter-prediction and intra-prediction technologies are used to remove redundancy between pictures so as to increase compression efficiency.
The method of encoding images using intra prediction predicts pixel values based on pixel correlation between blocks from pixel values in the blocks surrounding a current block, which have been already encoded, such as an upper block, a left block, an upper and left block, and an upper and right block in a current frame (or picture), and transmits their prediction errors.
In the intra-prediction encoding, among several prediction directions (horizontal, vertical, diagonal, or average, etc.), an optimal prediction mode (prediction direction) is selected to be suited for characteristics of an image to be encoded.
In the existing H.264/AVC standards, in the case that the intra-prediction encoding applies to a 4×4 pixel unit block, among nine prediction modes (prediction modes 0 to 8), one most appropriate prediction mode is selected every 4×4 pixel blocks, and the selected prediction mode (prediction direction) is encoded on a per-4×4 pixel block basis. Further, in the case that the intra-prediction encoding applies to a 16×16 pixel unit block, among four prediction modes (vertical prediction, horizontal prediction, average prediction, and planar prediction), one most appropriate prediction mode is selected every 16×16 pixel blocks, and the selected prediction mode (prediction direction) is encoded on a per-16×16 pixel block basis.
In the existing intra-prediction encoding, a predetermined number of prediction directions are predefined only for M×M square-type symmetrical pixel blocks (M=4, 8, or 16) to perform the intra-prediction encoding. That is, conventionally, M×M-size symmetrical partitioning only is applied for intra-prediction encoding so that a square-type symmetrical block is used as a basic unit for the intra-prediction encoding.